The invention relates to the use of satellite systems to control the guidance of vehicles and the positioning of towed implements; more particularly, steering control of agricultural, mining, and construction vehicles. For example, there is a need to accurately position agricultural vehicles and their implements (generally towed) used for plowing, listing, planting of crops, mechanically cultivating around crops and applying chemicals on and around crops. These techniques strive to minimize overlapping of rows and gaps between rows and reduce damage to crops by physical contact, and thereby result in higher crop yield, faster field operations and decreased costs to the farmer.
One approach for providing steering cues with Global Positioning System (GPS) and Differential Global Positioning Systems (DGPS) is with a light bar. The light bar typically supplies numerical and graphical information to an operator directing the desired steering. Information displayed in bright light emitting diode (LED) aid liquid crystal display (LCD) indicators are used both inside the cab or mounted outside on the hood of a vehicle to reduce eyestrain and remain within peripheral vision. Various numerical and graphical displays of cross track error (a positional error from a desired line), angle of approach (angle between current heading and desired line heading) and steering guides (angle to turn the steering wheel to move to and stay on the desired track), have been used.
Straight, or parallel, guidance uses two points, typically defined as A and B points and gives effective guidance along the line joining those points and lines offset from those lines; this offset is normally defined as the swath width of the implement. Contour guidance in several forms has been developed, with some generating a new line using data offset from the last driven line, and some using a more sophisticated approach of generating guidance continuously in real time to the closest point of all previously driven areas.
Dual frequency real-time kinematic (RTK) receivers have been used, with dual and triple antenna configurations coupled with combinations of Inertial Navigation System (INS) sensors, and gyros using sophisticated Kalman filtering techniques. Other systems utilize a three-axis inertial navigation system (INS) with a radar input for speed. These have been used for automatic steering of a main vehicle e.g., tractor and are often used on large farms where high value crops are grown and operators are not well trained in driving. Unfortunately, most inertial and gyro based systems are expensive and large.
Existing auto steer guidance methods solve the positioning of the vehicle in straight-line guidance mode, but do not necessarily address the positioning of the implement. In practice, large implements may be moved sideways by hitting rocks or differing soil conditions on each side as they are dragged, and the like. It will be appreciated that implements towed farther behind the vehicle are more susceptible to such deviation than those closely coupled to the vehicle.
Correction for positioning of the towed implement with DGPS has also been developed with the use of a movable hitch pin. This is used in both straight and contour line following. It is also used in a follow-me mode, where the magnitude of the radius of curvature, derived from the DGPS headings and speed, is used to proportionally move out the implement control mechanism, thus enabling the implement to follow in the tracks of the tractor and minimize crop damage. Correction for positioning of the towed implement with DGPS has also been developed with the use of a 3-point hitch and a steerable implement. In this instance, a second GPS antenna is attached to the implement with the cross track position used as the feedback error.
As farming becomes increasingly mechanized and farm implements faster and larger, so too does the difficulty of accurate positioning. The need is for a low cost solution to be used on many farm vehicles as a driver aid to enable the driver to concentrate on other tasks associated with field and implement operations to relieve the operator from the continuous monitoring and adjustment of steering.